1.

Comprehensiongiven below is followedby somemultiplechoicequestions.Eachquestion hasonecorrect option. Choosethe correctoption. In themodernperiodic tableelementsare arranged inorder of increasingatomicnumbers which is related to the electronicconfiguration . Dependingupon thetype of orbitalsreceiving the last electron the elements in the periodictable havebeen dividedinto four blocksviz, s, p, d and f. The modern periodictable consists of 7 periodsand 18groups.Each period begins withthe fillingof a new energy shell . Inaccordance withthe aufbau principle, the sevenperiods (1 to 7)have 2,8,8 ,18,18, 32 and 32elements respectively. Toavoidthe periodictable beingtoo long theseriesoff-blockelements calledlanthanoids and actinoidsare placed at thebottomof the main body ofthe periodictable.

Answer»

(i) The element with atomicnumber57belongs to
(i) s-block
( b)p-block
( c)d- block
( d) f- block
(ii) Thelast elementof the p-blockin 6th periodis representedby theoutermostelectronicconfiguration.
`(a)7 s^(2)7p^(6)`
`(b) 5f^(14)6d^(10)7s^(2) 7p^(0)`
`( c) 4f^(14)5d^(10)6s^(2)6p^(6)`
`( d)4f^(14)5d^(10)6s^(2)6p^(4)`
(iii) Whichof the elements whoseatomicnumbers are givenbelow , cannotbe accommodatedthe presentset up of the longformof the periodic table ?
( a) 107
( b)118
( c)126
( d)102
(iv) theelecronic configurationof the element which isjustabovethe elementwithatomicnumber43 inthe samegroup is ………..
`(a)1 s^(2)2 s^(2)2p^(6)3s^(2)3p^(6)3D^(5)4s^(2)`
`(b) 1 s^(2)2s^(2) 2p^(6)3s^(2)3p^(6)3d^(5)4s^(3)4p^(6)`
`( c)1 s^(2)2 s^(2)2p^(6)3s^(2)3d^(6) 4s^(2)`
`(d) 1 s^(2)2 s^(2)2p^(6)3s^(2) 3p^(6)3d^(6)4s^(2)`

Solution :(i)Refer tofootnote on page `3//14`
(ii) Eachperiodstartswith thefillingof electrons in a newprincipalenergyshell. Therefore6thperiod startswiththe fillingof 6s-orbital and end when6p-orbitals are completelyfilled. In between4f and5d- orbitals are filled in accordancewithaufbauprinciple. thusthe outermostelectronicconfigurationof thelastelementof the p- blockin the6thperiodis `6s^(2)4f^(14)5d^(10) ` or `4f^(14) 5d^(10)6s^(2)6p^(6)` Thusoption ( c) ISCORRECT.
(iii) Refer to Ansto Q.2 and Q.3. page `3//61`
(iv) The fifthperiod.Since the4thperiodhas 18elementthereforethe atomicnumberof theelementwhichliesimmediately abovethe elementwith atomicnumber43 is= 43 -18 = 25. Nowthe electronicconfigurationof elementwith Z= 25 is`1s^(2)2s^(2)2p^(6)3s^(2)3d^(5)4s^(2)` i.e.,option( a) iscorrect
Eachperiodends witha noblegas. Theatomicnumbersof noblegases(i.e.,group18 elements ) are2, 10 , 18 ,36 , 54and 86. Thereforeelementswith atomicwith atomicnumbers 35 (36-1) , 53 (54-1)and85 (86 -1) lie in a groupbeforenoblegasesi .e., halogens (group 17) elements.Thusthe element withatomicnumbers35,53 and85 are allhalogens i.e.,option( b) is correct.


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